I Would put 40 Volts into an LM317, Especially Not to get out 900mA or more.
It Will OVERHEAT.
I Would suggest Maybe 16 to 18 Volts input and set the output to 14.6 Volts.
The LM317 will also need a GOOD Heatsink.
And When you have it operating as a Constant Voltage Source, it is NOT a 1.5 Amp Constant current Output.
The Current Draw will be determined by the Charge on the Battery and your DC Supply.
If your battery is Low and your DC Source allows too much current, The LM317 will drive at the Full 1.5 amps.
When it gets too HOT, it will Shut down. NOT A GOOD SITUATION.
Typically it will take 12 Hours to Fully charge the battery, No Matter WHAT you do.
On a Dead or low Battery, the Charge rate will be high, But as the Battery Charges up, the Charge Current goes down.
The Final charge rate is in the LOW Milli-Amps.
It appears you have Very Little Electronic Knowledge.
** You might consider Emailing me your phone number and I could Explain all this better to you. I can call most countries for free.
Gary
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watzmann said:
something else i need to know : i'll connect the Vin of the LM317 to a power supply output 40 Voltage and 0.9A
in this case will the LM317 be able to supply at the Vout 1.5A as they tell in the datasheet ?
watzmann so you mean i can build my charger by adjusting the current to 14.5 using the LM317 ...... i looked at the datasheet it has a constant currant 1.5A
but are you sure that this will not damage my battery?
secondly , how can i know that my battery is fully charged ? ......
i know that i have to check the battery voltage but should be the voltage equal 13 or just 12 ?